System for transmitting and receiving a power line communication signal over the power bus of a power electronic converter

ABSTRACT

The present invention is concerned with a system for transmitting and/or receiving the control and sensing signals between the control units and the power electronic components. The system according to the present invention comprises: a transceiver adapted to modulate the communication signal on a communication signal frequency band, and a coupler connected to the power conductor and adapted to couple the modulated communication signal to the power conductor. The present invention also concerns a method for transmitting and receiving the control and sensing signals.

FIELD OF THE INVENTION

The present invention relates to the field of power electronicconverters, in particular to a communication system for exchanging thecontrol and sensing signals between the control units and the powerelectronic components. The present invention also concerns methods tofacilitate such connections.

BACKGROUND OF THE INVENTION

The conventional communication networks in power electronic convertersuse optical fibres for transmitting power electronic control and sensingsignals. When the communication signals are carried on optical fibres,the fast gate control (firing) signals can be reliably transmitted andwithstand large voltages.

However, this solution requires a high number of cables and connectors,which leads to high manufacturing costs and makes replacements of powerelectronic modules cumbersome. Also, ageing of fibres under high voltagestress may be critical.

WO 2006/039823, US 2012/207138 and WO 2012/143222 propose the use ofwireless transmission, i.e. radio or free space optical transmission, inPE converters to replace optical cabling.

DESCRIPTION OF THE INVENTION

Alternative communication technologies with simple and space savingstructure by using existing components of the power electronic converterare still of interest and the present invention introduces such analternative.

It is an objective of the invention to provide an alternative solutionto the wireless transmission of the communication signal, whichovercomes the problems of optical fibres as described before. Thisobjective is achieved by a method and a device according to theindependent claims. Preferred embodiments are evident from the dependentpatent claims.

The present invention provides a communication system for transmittingand/or receiving a communication signal through a power conductor of apower electronic converter with a plurality of converter modules,comprising a transceiver adapted to modulate the communication signal ona communication signal frequency band, and a coupler connected to thepower conductor and adapted to couple the modulated communication signalfrom or to the power conductor.

The communication signal comprises control and sensing signals between amain controller and a local controller of the power electronicconverter. In particular, a main controller of the power electronicconverter sends the control signal to the local controller of theconverter, and receives the sensing signal from the local controller.The main controller may be also called converter control unit while thelocal controller may be called switch control unit on a converter moduleof the power electronic converter.

According to the present invention, the communication signal istransmitted through the conductor of the power electronic converter,i.e. within the power electronic converter rather than on cable used fordistribution of electronic power to remote electric appliances. In otherwords, the present invention does not aim at providing a solution basedon power line communication as such but solution of using conductors ofthe power electronic converters. Hence, the modules within the powerelectronic converter can be controlled.

The term “modulate” comprises the meaning of modulating thecommunication signal when the transceiver acts as a transmitter, and themeaning of demodulating the communication signal when the transceiveracts as a receiver. Similarly, the term “couple” comprises the meaningof coupling the modulated communication signal to the power conductorwhen the transceiver acts as a transmitter, and the meaning ofdecoupling of the communication signal to be demodulated from the powerconductor when the transceiver acts as a receiver.

According to a further aspect, the present invention provides a powerelectronic converter comprising: a power conductor, a plurality ofconverter modules, and plurality of the above described communicationsystems connected with the converter modules for transmitting and/orreceiving the communication signal through or via the power conductor.

According to a further aspect, the present invention provides a methodfor transmitting and/or receiving a communication signal between a maincontroller and a local controller of a power electronic converter with aplurality of converter modules. The method comprises the steps of:modulating the communication signal, by a transceiver, on acommunication signal frequency band, coupling the modulatedcommunication signal to or from a power conductor of the powerelectronic converter, and transmitting or receiving the communicationsignal via the power conductor of the power electronic converter. Themain controller may both transmit and receive signal from localcontroller, and local controller may both receive and transmit signal tomain controller.

In particular, in case that the transceiver acts as a transmitter, themethod is for transmitting the communication signal of the powerelectronic converter with a plurality of converter modules, andcomprises the steps of: modulating the communication signal, by atransceiver, on a communication signal frequency band; coupling, by thecoupler, the modulated communication signal to a power conductor of thepower electronic converter. In case that the transceiver acts as areceiver, the method is for receiving the communication signal of thepower electronic converter with a plurality of converter modules, andcomprises the steps of: decoupling, by the coupler, the demodulatedcommunication signal from the power conductor; and demodulating thecommunication signal, by a transceiver, on the communication signalfrequency band.

Preferably, the coupler comprises a capacitive coupler or an inductivecoupler. The couple may comprises more than one capacitive or indicativecoupler. With more than one coupler, the system enables multipleredundant transmission and reception of the communication signals.

Preferably, the communication signal is modulated on the communicationsignal frequency band that is different to the frequency band of thepower waveform.

Preferably, the system further comprises: a high frequency bypassconnected in parallel to a power electronic switch of the powerelectronic converter, and adapted to the communication signal frequencyband.

The present invention takes advantage of using the existing electricpower buses for transmission of the control and sensing signal, thereby,saving a separate communication network for carrying these signals.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject-matter of the present invention will be explained in moredetail in the following text with reference to preferred exemplaryembodiments which are illustrated in the attached drawings, in which:

FIG. 1 schematically shows a typical topology of an AC-DC-AC modularmultilevel electronic power converter;

FIG. 2 schematically shows a typical communication architecture of amedium voltage power electronic converter, where the control and sensorsignals are exchanged between the main controller and the localcontrollers; and

FIG. 3 schematically shows power line communication, PLC, in a PEconverter according to the present invention, in which the PLCtransceivers, PLC-TRX, capacitive and inductive couplings, and highfrequency gate bypass are shown.

The reference symbols used in the drawings, and their primary meanings,are listed in summary form in the list of designations. In principle,identical parts are provided with the same reference symbols in thefigures.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows the topology of a typical Power Electronic 1 converter, PEconverter. The PE switches, i.e. power semiconductors, control thecurrent flow through the connected power buses. Using appropriatecontrol commands to the switches, the AC power at the input (V_(R),V_(S), V_(T)) is converted to another AC power waveform at the output(V_(U), V_(V), V_(W)).

The control and communication infrastructure generates and transmits thecontrol signals, e.g. gate signals, to the PE switches. FIG. 2 showssuch communication architecture. The control and sensor signals areexchanged between a main controller 100 and local controllers 200located in different cabinets over the communication network 110. Alocal controller 200 together with a number of PE switches make up aPower Electronic Building Block, PEBB. The local connections within aPEBB from the local controller to its PE switches use electrical oroptical wires 120.

The present invention takes advantage of the fact that the PE switches50 in a PE converter are connected to electric power buses, which carrythe electric currents to be switched, see FIG. 1. The communication tothe distributed control units, i.e. local controller, LCs, associated tothe PE switches may thus utilize these power buses as the communicationmedium, using power line communication.

FIG. 3 shows that the power line communication transceivers couple theircommunication signals to and from the power buses, according to thepresent invention. The power bus serves as a communication mediumcarrying the control and sensor signals in the form of PLC signals, aswell as the (AC) power. To minimize interference from the powerwaveform, with strong harmonics at up to several kHz, PLC signals aremodulated to a different frequency band, e.g. of tens of kHz to tens ofMHz, and can thus be separated from the power waveform by band-pass orhigh-pass filtering. The PLC signals have much lower power, of mV toseveral Volts peak, than the power waveform. In other words, themodulated PLC signals will be transmitted by the electronic couplershaving band-pass or high-pass filter characteristic.

The power line signal coupling may be either capacitive or inductive. Asan example, the main controller, MC PLC-TRX, 21 is shown with capacitivecoupling between the power buses of phases R and S. The capacitivecoupling has in general better performance than inductive coupling, butrequires space for high voltage capacitors and connectors to pairs ofcables, i.e. power buses.

With inductive couplers, the PLC signals are coupled transformer-likeusing wire coils around the power bus. In FIG. 3, a local controller, LCPLC-TRX, 31 is shown with inductive coupling. Inductive couplers may beeasier to install, but coupling performance depends on the mechanicalarrangements and, if a magnetic transformer core is used, on itsferromagnetic properties, in particular, its non-linearity due tosaturation.

The above example describes the case where the master controller usescapacitive coupling and the local controller uses inductive coupling.Any combination of controllers and PLC couplers is possible.

Due to the converter operation, parts of a power branch to which acontroller is connected may, in a given period of time determined by theswitching states in the converter, be in non-conducting state, i.e. whenthe switch is temporarily turned off, no current may flow through thatsection of the bus. This would affect PLC communication. Hence,preferably, depending on the characteristics of the PE switch, a highfrequency (HF) bypass 40 for the PLC signals is introduced in parallelto the PE switches, in order to achieve acceptable communicationreliability. This is shown in FIG. 3 as capacitors 40. The HF bypass 40lets the PLC signal bypass the PE switch, irrespective of the state ofthe PE switch.

In a preferred embodiment, a PLC transceiver may employ more than onecoupler connected to different coupling points on the power bus, asshown as an example in FIG. 3 for the LC PLC-TRX 31. This allowsmultiple redundant transmission and reception of the PLC communicationsignal. In particular, in what is known as reception diversity, the PLCreceiver may select or combine multiple signals received from differentcouplers for best performance.

To further mitigate interference from the power waveform, the PLCreceiver may employ adaptive noise cancelling. That is, if the powerwaveform is known by the PLC receiver, e.g. from separate measurementsor from separate control information, this known interference can becancelled, i.e. subtracted, from the total received signal. This furtherimproves the quality of the desired received PLC signal.

The high frequency gate bypass may be realized by the inherent straycapacitances of the PE switch, typically flat silicon semiconductorchips or wafers. Thus, no additional circuitry is required. This dependson the high frequency impedance of the PE devices.

Where receive-only nodes suffice, e.g. in the case where localcontrollers are designed such they only need to receive controlinformation and do not need to transmit any data, PLC receiver couplingmay employ the principle of the Fibre Optic Current Sensor, FOCS. SuchFOCS coupling may facilitate PLC installation in a PE converterconsiderably. However, accuracy and high frequency performance of suchFOCS couplers should be designed accordingly.

According to a further aspect of the present invention, the PLC couplersshould fit the available space and mechanical arrangements. Highinterference from the PE operation may affect the reliability of PLCtransmission. The data rate supported by the PLC communication dependson the impedance properties of the power bus at high frequencies, and onEMC restrictions on emissions.

While the invention has been described in detail in the drawings andforegoing description, such description is to be considered illustrativeor exemplary and not restrictive. Variations to the disclosedembodiments can be understood and effected by those skilled in the artand practising the claimed invention, from a study of the drawings, thedisclosure, and the appended claims. In the claims, the word“comprising” does not exclude other elements or steps, and theindefinite article “a” or “an” does not exclude a plurality. The merefact that certain elements or steps are recited in distinct claims doesnot indicate that a combination of these elements or steps cannot beused to advantage, specifically, in addition to the actual claimdependency, any further meaningful claim combination shall be considereddisclosed.

1. System for transmitting and/or receiving a communication signal via apower conductor of a power electronic converter with a plurality ofconverter modules, comprising: a transceiver adapted to modulate thecommunication signal on a communication signal frequency band, and acoupler connected to the power conductor and adapted to couple themodulated communication signal to or from the power conductor.
 2. Systemaccording to claim 1, wherein the coupler comprises a capacitive couplerand/or an inductive coupler.
 3. System according to claim 1, wherein thecommunication signal frequency band is different to the frequency bandof the power waveform.
 4. System according to claim 3, furthercomprises: a high frequency bypass connected in parallel to a powerelectronic switch of the power electronic converter and adapted to thecommunication signal frequency band.
 5. Power electronic convertercomprising: a power conductor; a plurality of converter modules; and aplurality of systems connected with the converter modules fortransmitting and/or receiving the communication signal via the powerconductor, each of the plurality of systems comprises: a transceiveradapted to modulate the communication signal on a communication signalfrequency band; and a coupler connected to the power conductor andadapted to couple the modulated communication signal to or from thepower conductor.
 6. Method for transmitting and/or receiving acommunication signal between a main controller and a local controller ofa power electronic converter with a plurality of converter modules,comprising: modulating the communication signal, by a transceiver, on acommunication signal frequency band, coupling the modulatedcommunication signal, by a coupler, to or from a power conductor of thepower electronic converter, and transmitting or receiving thecommunication signal via the power conductor of the power electronicconverter.
 7. Method according to claim 6, wherein the coupler comprisesa capacitive coupler and/or an inductive coupler.
 8. Method according toclaim 6, wherein the communication signal frequency band is different tothe frequency band of the power waveform.
 9. Method according to theclaim 8, further comprises the step of: connecting a high frequencybypass in parallel to a power electronic switch of the power electronicconverter, and bypassing the communication signal on the communicationsignal frequency band.
 10. System according to claim 2, wherein thecommunication signal frequency band is different to the frequency bandof the power waveform.
 11. Method according to claim 7, wherein thecommunication signal frequency band is different to the frequency bandof the power waveform.
 12. System according to claim 5, wherein thecoupler comprises a capacitive coupler and/or an inductive coupler. 13.System according to claim 5, wherein the communication signal frequencyband is different to the frequency band of the power waveform. 14.System according to claim 5, further comprises: a high frequency bypassconnected in parallel to a power electronic switch of the powerelectronic converter and adapted to the communication signal frequencyband.